1. Field of the Invention
The present invention relates to a load control system for a plurality of electrical loads in a building, and more particularly, to a load control system for automatic control of the electrical loads to reduce the total power consumption of the load control system, and manual control of the electrical loads to improve occupant comfort.
2. Description of the Related Art
Reducing the total cost of electrical energy is an important goal for many electricity consumers. The customers of an electrical utility company are typically charged for the total amount of energy consumed during a billing period. However, since the electrical utility company must spend money to ensure that its equipment (e.g., an electrical substation) is able to provide energy in all situations, including peak demand periods, many electrical utility companies charge their electricity consumers at rates that are based on the peak power consumption during the billing period, rather than the average power consumption during the billing period. Thus, if an electricity consumer consumes power at a very high rate for only a short period of time, the electricity consumer will face a significant increase in its total power costs.
Therefore, many electricity consumers use a “load shedding” technique to closely monitor and adjust (i.e., reduce) the amount of power presently being consumed by the electrical system. Additionally, the electricity consumers “shed loads”, i.e., turn off some electrical loads, if the total power consumption nears a peak power billing threshold established by the electrical utility. Prior art electrical systems of electricity consumers have included power meters that measure the instantaneous total power being consumed by the system. Accordingly, a building manager of such an electrical system is able to visually monitor the total power being consumed. If the total power consumption nears a billing threshold, the building manager is able to turn off electrical loads to reduce the total power consumption of the electrical system.
Many electrical utility companies offer a “demand response” program to help reduce energy costs for their customers. With a demand response program, the electricity consumers agree to shed loads during peak demand periods in exchange for incentives, such as reduced billing rates or other means of compensation. For example, the electricity utility company may request that a participant in the demand response program shed loads during the afternoon hours of the summer months when demand for power is great. An example of a lighting control system that is responsive to demand response commands is described in greater detail in commonly-assigned U.S. Pat. No. 7,747,357, issued Jun. 29, 2010, entitled METHOD OF COMMUNICATING A COMMAND FOR LOAD SHEDDING OF A LOAD CONTROL SYSTEM, the entire disclosures of which are hereby incorporated by reference.
Some prior art lighting control systems have offered a load shedding capability in which the intensities of all lighting loads are reduced by a fixed percentage, e.g., by 25%, in response to an input provided to the system. The input may comprise an actuation of a button on a system keypad by a building manager. Such a lighting control system is described in commonly-assigned U.S. Pat. No. 6,225,760, issued May 1, 2001, entitled FLUORESCENT LAMP DIMMER SYSTEM, the entire disclosure of which is hereby incorporated by reference.
Some prior art load control systems have provided for control of both the intensities of electrical lighting loads (to control the amount of artificial light in a space) and the positions of motorized window treatments (to control the amount of daylight entering the space). Such load control systems have operated to achieve a desired lighting intensity on task surfaces in the space, to maximize the contribution of the daylight provided to the total light illumination in the space (i.e., to provide energy savings), and/or to minimize sun glare in the space. An example of a load control system for control of both electrical lighting loads and motorized window treatments is described in greater detail in commonly-assigned U.S. Pat. No. 7,111,952, issued Sep. 26, 2006, entitled SYSTEM TO CONTROL DAYLIGHT AND ARTIFICIAL ILLUMINATION AND SUN GLARE IN A SPACE, the entire disclosure of which is hereby incorporated by reference. In addition, prior art heating, ventilation, and air-conditioning (HVAC) control systems allow for control of a setpoint temperature of the HVAC system to provide for control of the present temperature in a building and may operate to minimize energy consumption.
It is desirable to automatically control the lighting intensities of lighting loads, the positions of motorized window treatments, and the temperature of the building in a single load control system in order to reduce the total power consumption of the load control system. However, when automatically controlling three or more variables of a load control system to ultimately control three or more parameters of the building where there is some non-linearity in the relationships between the variables and the parameters, unpredictability (i.e., deterministic chaos) may exist in the system. For example, if a load control system automatically controls the intensities of electrical lighting loads, the positions of motorized window treatments, and the setpoint temperature of an HVAC system in order to ultimately control the total light intensity, the present temperature, and the total energy consumption of a space in the building, the resulting operation of the system may disordered and random to a user of the system. Accordingly, the system may not be able to automatically control these variables to produce the desired and optimum control of the variables in the building.